1. Field of the Invention
The present invention relates to an image processing method of combining a plurality of images, and more particularly, to an image processing method capable of effectively eliminating the effects of moving objects when combining a plurality of images.
2. Description of the Prior Art
A ratio of the highest luminance to the lowest luminance in a scene is defined as a dynamic range of the scene. Typically, the dynamic range of the real world is over 50,000:1, and the dynamic range of the human vision system (HVS) is over 10,000:1. Moreover, in some specific lighting condition, human eyes can differentiate some 10,000 colors. Thus, human eyes can detect different luminance in the real word to a fairly satisfactory degree.
Image capturing devices (such as cameras) or image display devices (such as computer displays) commonly used for processing images, however, have a dynamic range far less than the dynamic range of the real world. Therefore, those image devices are unable to capture or display details of high luminance (i.e. over-exposure) or low luminance (i.e. under-exposure) regions in a scene in some condition. For example, an image capturing device or an image display device having a dynamic range of 255:0 may treat all pixels in a high luminance region in a scene as white pixels having grayscale values of (255, 255, 255), or treat all pixels in a low luminance region in a scene as black pixels having grayscale values of (0, 0, 0). In other words, those image devices are unable to record details of high luminance or low luminance regions in a scene.
Generally, an image having a high dynamic range is called a high dynamic range (HDR) image. Presently, there is no simple and direct way to capture or display an HDR image. Therefore, an alternative method to execute multiple exposures in a scene to capture a plurality of low dynamic range (LDR) images and then combine the LDR images into an HDR image of the scene is provided.
Inevitably, there is always a time lag between the timings of capturing the plurality of LDR images. During the time lag, random objects in the captured scene may move and the positions of the random object may be different in the plurality of LDR images. When combining the plurality of LDR images to generate the HDR image, the random objects moving during the time lags may cause undesired effects (e.g. ghosts and broken objects) in the HDR image. Thus, how to eliminate the undesired effects generated by the moving objects becomes a topic to be discussed.